1. Field of the Invention
The present invention generally relates to an apparatus for processing embroidery data utilized by a sewing machine and particularly to such an apparatus for producing data used for embroidering an area such as a character or pattern by forming zigzag stitches with a predetermined width along a line or lines defining the character or pattern.
2. Related Art Statement
The Assignee of the present U.S. patent application has filed Japanese Patent Application No. 1-276700 on Oct. 24, 1989, which discloses an apparatus for automatically processing embroidery data used for embroidering a character or pattern (hereinafter referred to as the "figure") by forming zigzag stitches having a predetermined width along a line or lines (hereinafter referred to as the "line") defining the figure.
The proposed apparatus processes embroidery data by utilizing sets of point data indicative of positions of a series of points on a line, and width data indicative of a predetermined width of the zigzag stitches to be formed along the line. The line may be either a polygonal line or a curved line. In the former case, the series of points consist of vertices of the polygonal line, and in the latter case the series of points consist of vertices of a polygonal line approximating the curved line. The apparatus divides a figure or embroidery area defined by a line and a zigzag stitch width, into a plurality of blocks each having a shape of trapezoid (hereinafter, referred to as the "trapezoid blocks" or, when appropriate, "trapezoids"). More specifically described, the apparatus determines a first and a second virtual straight line with respect to each of straight line segments each of which connects between a corresponding one of pairs of adjacent two points out of a series of points on the line, such that the first and second virtual lines are parallel to, and respectively located on both sides of, the each line segment, and are spaced apart from each other by a distance equal to the zigzag stitch width, and produces block data representative of a trapezoid block, namely, trapezoid bounded by (a) a first base connecting between a first intersection between the first virtual line corresponding to the each line segment and the first virtual line corresponding to one of two line segments adjacent to, and on both sides of, the line segment, and a second intersection between the first virtual line corresponding to the each line segment and the first virtual line corresponding to the other of the two line segments, (b) a second base connecting between a third intersection between the second virtual line corresponding to the each line segment and the second virtual line corresponding to the above-indicated one of the two line segments, and a fourth intersection between the second virtual line corresponding to the each line segment and the second virtual line corresponding to the above-indicated other of the two line segments, (c) a first leg connecting between the first and third intersections, and (d) a second leg connecting between the second and fourth intersections. Sets of block data representative of trapezoid blocks as divisions of the figure produced may be utilized as a batch of embroidery data for embroidering the figure. For embroidering the figure by forming zigzag stitches along the line defining the figure, it is necessary to produce sets of stitch position data representative of stitch positions where a stitch needle pieces a workpiece or fabric. An automatic sewing machine may be adapted to produce stitch position data by utilizing block data, while at the same time forming zigzag stitches according the stitch position data produced.
Thus, the proposed apparatus automatically produces embroidery data by dividing a figure having a predetermined width into a plurality of trapezoid blocks, each of which is to be filled with zigzag stitches having the predetermined width.
However, the above-identified apparatus suffers from a problem that, in the event that a length of a line segment connecting between adjacent two points out of a series of points is small in comparison with a zigzag stitch width, a number of stitches may overlap each other, thereby failing to provide an embroidery having an excellent external appearance. In the event that the distance between adjacent two points is great in comparison with the zigzag stitch width, as shown in FIG. 21, for example, zigzag stitches formed by alternately connecting the two bases, AC and BD, of trapezoid block, ABCD, do not overlap each other, thereby providing an excellent embroidery, because block ABCD is a normal trapezoid whose two legs, AB and CD, do not intersect each other. On the other hand, in the event that the distance between adjacent two points is small relatively to the zigzag stitch width, as shown in FIG. 22, for example, zigzag stitches formed by alternately connecting the two bases, AC and BD, of trapezoid block, ABCD, overlap each other, thereby failing to provide an excellent embroidery, because block ABCD is an abnormal trapezoid whose two legs, AB and CD, intersect each other and which, therefore, consists of two triangles connected to each other at their common vertex.